Performance characteristics of the first Food and Drug Administration (FDA)-cleared digital droplet PCR (ddPCR) assay for BCR::ABL1 monitoring in chronic myelogenous leukemia

Chronic myelogenous leukemia (CML) is a hematopoietic stem cell malignancy that accounts for 15-20% of all cases of leukemia. CML is caused by a translocation between chromosomes 9 and 22 which creates an abnormal fusion gene, BCR::ABL1. The amount of BCR::ABL1 transcript RNA is a marker of disease progression and the effectiveness of tyrosine kinase inhibitor (TKI) treatment. This study determined the analytical and clinical performance of a droplet digital PCR based assay (QXDx BCR-ABL %IS Kit; Bio-Rad) for BCR::ABL1 quantification. The test has a limit of detection of MR4.7 (0.002%) and a linear range of MR0.3-4.7 (50-0.002%IS). Reproducibility of results across multiple sites, days, instruments, and users was evaluated using panels made from BCR::ABL1 positive patient samples. Clinical performance of the assay was evaluated on patient samples and compared to an existing FDA-cleared test. The reproducibility study noted negligible contributions to variance from site, instrument, day, and user for samples spanning from MR 0.7-4.2. The assay demonstrated excellent clinical correlation with the comparator test using a Deming regression with a Pearson R of 0.99, slope of 1.037 and intercept of 0.1084. This data establishes that the QXDx™ BCR-ABL %IS Kit is an accurate, precise, and sensitive system for the diagnosis and monitoring of CML.

Assessment of droplet digital polymerase chain reaction for measuring BCR-ABL1 in chronic myeloid leukaemia in an international interlaboratory study

Measurement of BCR activator of RhoGEF and GTPase -ABL proto-oncogene 1, non-receptor tyrosine kinase (BCR-ABL1) mRNA levels by reverse transcription quantitative polymerase chain reaction (RTqPCR) has been critical to treatment protocols and clinical trials in chronic myeloid leukaemia; however, interlaboratory variation remains a significant issue. Reverse transcriptase droplet digital PCR (RTddPCR) has shown potential to improve testing but a large-scale interlaboratory study is required to definitively establish this. In the present study, 10 BCR-ABL1-positive samples with levels ranging from molecular response (MR)^1·0 -MR^5·0 were tested by 23 laboratories using RTddPCR with the QXDX BCR-ABL %IS kit. A subset of participants tested the samples using RTqPCR. All 23 participants using RTddPCR detected BCR-ABL1 in all samples to MR^4·0 . Detection rates for deep-response samples were 95·7% at MR^4·5 , 78·3% at MR^4·7 and 87·0% at MR^5·0 . Interlaboratory coefficient of variation was indirectly proportional to BCR-ABL1 level ranging from 29·3% to 69·0%. Linearity ranged from 0·9330 to 1·000 (average 0·9936). When results were compared for the 11 participants who performed both RTddPCR and RTqPCR, RTddPCR showed a similar limit of detection to RTqPCR with reduced interlaboratory variation and better assay linearity. The ability to detect deep responses with RTddPCR, matched with an improved linearity and reduced interlaboratory variation will allow improved patient management, and is of particular importance for future clinical trials focussed on achieving and maintaining treatment-free remission.

Abstract 6483: Performance characteristics of the first FDA-cleared droplet digital PCR (ddPCR) IVD assay for monitoring chronic myelogenous leukemia

Introduction: Chronic myelogenous leukemia (CML) is a cancer of myeloid cells that accounts for 15-20% of all cases of leukemia. Most CML cases are caused by a translocation between chromosomes 9 and 22 which creates an abnormal fusion gene, BCR-ABL1. The BCR-ABL1 gene expresses an abnormal tyrosine kinase protein that causes unregulated growth and survival of granulocytes. CML is treated with TKIs (tyrosine kinase inhibitors). The concentration of BCR-ABL1 transcript RNA is a marker of disease progression and the effectiveness of TKI treatment.Bio-Rad's QXDx BCR-ABL %IS Kit is an in vitro diagnostic test for the quantification of BCR-ABL transcripts in total RNA from whole blood from individuals diagnosed with Chronic Myeloid Leukemia expressing BCR-ABL1 Fusion transcript types e13a2 and/or e14a2.

Materials and Methods: The QXDx BCR-ABL %IS Kit is a newly launched FDA-approved ddPCR assay from Bio-Rad Laboratories. Reproducibility of results across multiple sites, days, instruments, and users was evaluated using contrived samples consisting of BCR-ABL positive patient samples mixed with negative patient samples. Clinical performance of the kit was evaluated on patient samples, and compared to an already existing FDA-approved test. Clinical performance was further tested in the College of American Pathologists challenge.

Results: The reproducibility study noted negligible contributions to variance from site, instrument, day, and user for samples spanning from MR 0.7-4.2. The mean between the QXDx™ BCR-ABL %IS Kit and the comparator test using a Bland-Altman analysis was 0.16 MR units. The limits of agreement between the two methods indicate that the difference between the two methods should be between 0.47 and -0.14 MR on 95% of tested samples. The QXDx™ BCR-ABL %IS assay demonstrated excellent correlation with the comparator test using a Weighted Deming regression with a Pearson R correlation coefficient of 0.99, slope 1.037 and intercept of 0.1084. College of American Pathologists(CAP) challenges (n=6) were conducted from 2016-2019, QXDx™ BCR-ABL %IS system results were regressed vs the mean values published by CAP yielded a slope of 1 and R2=0.99.

Conclusions: The QXDx™ BCR-ABL %IS Kit on the QXDx™ AutoDG™ Droplet Digital PCR System can be used safely and effectively in the laboratory on t(9;22) positive CML patients for monitoring of treatment with Tyrosine Kinase Inhibitors (TKIs).

Citation Format: Dawne N. Shelton, Prasanthi Bhagavatula, Nathan Sepulveda, Lan Beppu, Jerald Radich. Performance characteristics of the first FDA-cleared droplet digital PCR (ddPCR) IVD assay for monitoring chronic myelogenous leukemia [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6483.

Unmet Dental Care Need and Associated Barriers by Race/Ethnicity among US Adults

INTRODUCTION

Ability to access needed dental care may vary among population subgroups. We assessed 1) the differences in the proportions of adults who reported unmet dental care needs in the past 12 months and the associated barriers (structural, financial, and cognitive) in 2015 to 2016 versus 2003 to 2004 by race/ethnicity and 2) the subgroups that are more likely to report unmet dental care needs.

METHODS

Data of 10,029 respondents aged ≥19 y from the 2003-2004 and 2015-2016 National Health and Nutrition Examination Surveys were used. Chi-square tests assessed the differences in the proportions of adults who reported not getting the needed dental care between the periods. A multiple logistic regression model was run to identify characteristics that were significantly associated with unmet need after adjusting for other factors.

RESULTS

Overall, 19.4% of the adults reported an unmet dental care need in 2015 to 2016, as compared with 21% in 2003 to 2004. The overall unmet dental care need decreased only in the Hispanic groups (34% to 28%, P = 0.045) between 2003-2004 and 2015-2016. Between the periods, unmet need decreased among Hispanics aged 19 to 64 y (35% to 28%, P = 0.02), Hispanics with some college education or above (33.5% to 21.0%, P = 0.008), and nonpoor Hispanic adults (29.8% to 20.4%, P = 0.048). No significant differences were observed in the proportions of adults reporting structural (P = 0.09), financial (P = 0.86), or cognitive (P = 0.07) barriers between the periods. When compared with their counterparts, nonelderly adults, women, Hispanics, adults with a high school education, those with less than a high school education, and poor adults were significantly more likely to report unmet dental care needs.

CONCLUSIONS

Racial and ethnic disparities in accessing and receiving the needed dental care still exist. Financial barriers to dental care are the most commonly cited reasons for not getting the needed dental care.

KNOWLEDGE TRANSFER STATEMENT

The results of the study will inform policy makers, public health planners, and dental professionals about subgroups that still face difficulty in receiving the dental care they need. Policy makers should develop new policies to mitigate the financial barriers that are still prevalent. Dental professionals can mitigate the public's cognitive and financial barriers by educating the community through outreach programs and by providing services to low-income populations at reduced charges or through alternative payment plans.

Retrolinkin, a membrane protein, plays an important role in retrograde axonal transport

Retrograde axonal transport plays an important role in the maintenance of neuronal functions, but the mechanism is poorly defined partly because the constituents of the retrograde transport system and their interactions have yet to be elucidated. Of special interest is how dynein/dynactin motor proteins interact with membrane cargoes. Here, we report that an endosomal vesicle protein, termed retrolinkin, functions as a receptor tethering vesicles to dynein/dynactin through BPAG1n4. Retrolinkin, a membrane protein highly enriched in neuronal endosomes, binds directly to BPAG1n4. Deletion of retrolinkin membrane-association domains disrupts retrograde vesicular transport, recapitulating the BPAG1 null phenotype. We propose that retrolinkin acts with BPAG1n4 to specifically regulate retrograde axonal transport. Our work lays the foundation for understanding fundamental issues of axonal transport and provides insights into the molecular mechanisms underlying human neurodegenerative disorders.